Answered question
Is there an option to add a second line to an account? If so, are there discounts for having multiple plans on the same bill.
Yes, you can add extra lines to the same account. I have not yet seen anything to indicate that there will be a discount for addtional lines.
Other answers
Allison is correct :) you can add as many lines -no additional discounts for adding more lines, the only discount is adding them in the first place with Fizz's awesome launch prices.